1. Field of the Invention
The present invention relates to a playback apparatus for a rotary recording medium, and in particular to a playback apparatus for a rotary recording medium for reproducing information signals such as video signals representing a still picture recorded on a rotary magnetic recording medium such as a magnetic disk.
2. Description of the Related Art
There has been recently developed an electronic still camera system including an image pickup device, such as a solid-state image pickup device or tube, and a recorder utilizing as a recording medium a low-price magnetic disk having a relatively large recording capacity, in which an electronic still picture of an object is recorded on a rotating disk, and the recorded picture is reproduced by use of a separate television system, a printer, or the like.
However, recording media utilized in such magnetic recording, especially magnetic disks are likely to cause a tracking failure due to the anisotropy, eccentricity, thermal expansion, and the like. Consequently, a track adjacent to the track to be scanned for the reproduction is erroneously scanned, which results in crosstalk of signals reproduced.
In order to overcome this difficulty, there has been adopted a method in which the tracking servo is applied when recording information so as to record tracking signals. The tracking servo is effected by use of the recorded tracking signals when reproducing the information. However, a tracking servo mechanism requiring a precise control cannot be practically incorporated in a light-weight, compact recording apparatus such as a camera.
There has been a method utilizing a guard band system or an FM azimuth system as a recording scheme so as to compensate for above-stated operations. That is, the playback head is prevented from scanning the adjacent wrong track due to a slight tracking failure during the playback, and the signals, even though scanned on the adjacent track, could be blocked.
On the other hand, there has been utilized a method called an envelope peak detecting autotracking system. In accordance with this system, the recording head is moved with a predetermined pitch by use of a stepping motor without tracking servo when recording information, whereas an envelope of the output signals reproduced from a track is detected and the optimum track position is identified based on the peak position of the envelope, thereby accomplishing the tracking servo on the operation for reproducing the recorded signals.
In an electronic still camera system, a rotary magnetic recording medium used includes, for example, a magnetic disk of which the diameter is about 50 mm, and the track pitch, track width, and guard band width are selected to be about 100 .mu.m, 50 .mu.m to 60 .mu.m, and 40 .mu.m to 50 .mu.m, respectively, in order to record information of 50 tracks of the disk surface. When installed in a recording or playback apparatus, a magnetic disk is rotated at a constant rotating rate of, for example, 3,600 revolutions per minute (rpm) so as to record or reproduce image signals at a field or frame rate.
Such a thin, compact magnetic disk having a relatively small diameter is usually housed in a mold package made of materials such as plastic. That is, the disk package is installed in a disk mounting unit of a recording or playback apparatus, and is rotated in the same state for recording or reproducing information.
In order to select an appropriate track in a playback operation, it is required to correctly identify and to display tracks or the track numbers thereof.
In a recording unit, when a signal dropout occurs on a track of a magnetic disk, the track is skipped to record information on the next appropriate track in some cases. Consequently, in a playback unit so configured as to identify a track number simply based on the distance traveled by the playback head, a faulty track on which video signals have not been recorded is recognized to be a valid track, and the track number of this track is thus displayed. This may become inconvenient in the operation of a playback device which rapidly selects and displays a picture associated with a desired frame number.
Even if the playback head is moved onto such an unrecorded track when reproducing signals from a magnetic disk, not fully recorded up to the limit of the disk capacity, by use of a playback device reproducing the recorded information by skipping the unrecorded track, the playback head can be continuously moved until it reaches a mechanical limit position for the head travel. This may cause the associated mechanism to be damaged unless certain control is provided to the playback head movement.